1. Field of the Invention
The present invention relates to a so-called bending zoom lens system.
2. Description of Related Art
In recent years, there has been a strong demand for digital cameras to be further miniaturized (especially in regard to a slimmer body design). A bending optical system which is provided with reflective members such as prisms or reflection mirrors that bend the optical path within the lens system is known in art as arrangement that can achieve a slimmer body design. For example, in Japanese unexamined patent application No. 2006-154702, a zoom lens system is disclosed which achieves a reduction in the number of lens elements and a reduction in the overall length of the zoom lens system (a slimmer body design) by providing reflection prisms, each having a refractive power, at the object side and at the image side of the zoom lens system, respectively, in which each of the reflection prisms shares the optical function of an optical lens element.
In order to achieve miniaturization of the zoom lens system, it is essential to reduce the overall length of the zoom lens system. However, if attempts are made to increase the zoom ratio by extending the focal length at the long focal length extremity toward the telephoto side in order to achieve a higher zoom ratio, miniaturization of the zoom lens system becomes difficult since the overall length of the zoom lens system increases. Accordingly, in order to achieve a compact zoom lens system having a high zoom ratio, it is desirable to reduce the focal length at the short focal length extremity so as to attain a wider angle-of-view.
In the zoom lens system disclosed in the above-mentioned Japanese unexamined patent application No. 2006-154702, a low-dispersion material is used for a reflection prism provided at the image side in order to reduce chromatic aberration (by suppressing the amount of chromatic aberration that occurs at the reflection prism itself); however, in such an arrangement, if the focal length is reduced and the angle-of-view widened at the short focal length extremity, the canceling-out effect of the image side reflection prism, by correcting lateral chromatic aberration that occurs at the lens group at the object side, is reduced. Furthermore, since the first lens group is configured only of a single (another) reflection prism having a refractive power, the lateral chromatic aberration in the case where the focal length is reduced and a wider angle-of-view is attained cannot be sufficiently corrected, so that it is difficult to achieve a high zoom ratio considering the balance of the aberrations. In fact, the zoom lens system of Japanese unexamined patent application No. 2006-154702 only has a zoom ratio of approximately 2:1, which cannot be said to satisfy the high-specification needs of the market.